Method and system for multiuser wireless communications using anti-interference to increase transmission data rate

ABSTRACT

A method and system for multi-user wireless communications between a sender and a receiver enables effective blocking of interference signals by other senders and improving the channel data rate. The receiver uses two or more receiving devices, such as antennas or smart antennas, to receive multiple wireless input signals. By performing a noise-transparent autocorrelation matching analysis on the multiple input signals, the receiver derives an anti-interference filter for interference-blocking action, without the need for information of the interfering and its transmission channel. In a multi-user environment, the noise-transparent autocorrelation matching analysis is implemented by the Autocorrelation Division Multiple Access (ADMA) system that includes the design and the implementation of ADMA code, the ADMA encoder, the ADMA algorithm and the ADMA decoder.

RELATED APPLICATIONS

This application claims the priority of U.S. Provisional PatentApplication No. 60/940,330 filed May 25, 2007. This is also acontinuation-in-part of U.S. patent application Ser. No. 12/123,992,filed May 20, 2008, which is a continuation of U.S. patent applicationSer. No. 11/002,161, now issued U.S. Pat. No. 7,376,394 entitled “METHODAND SYSTEM FOR WIRELESS COMMUNICATIONS USING ANTI-INTERFERENCE TOINCREASE DATA TRANSMISSION RATE,” which claims priority to U.S.Provisional Patent Application No. 60/526,512, filed Dec. 3, 2003, allof which are hereby incorporated by reference in their entirety foreverything that they describe.

FIELD OF THE INVENTION

This invention relates generally to wireless communications, and moreparticularly to Autocorrelation Division Multiple Access (ADMA) systemand autocorrelation matching algorithms that blocks multiple accessinterference and co-channel interference to achieve improved channeldata rate and increased number of users within limited spectrum.

BACKGROUND

Wireless communications have become a major way of communications and inmany applications are replacing conventional land-based communicationsystems. There are many kinds of wireless communication systems, such asthe cellular phone system, the wireless LAN, and the WiMAX. The mostcommonly used system is the cellular system, and the other wirelesscommunication systems such as WiFi and WiMax are growing rapidly.

The users of a wireless channel may be, for instance, a cellular phone,a laptop computer, etc. Many users may share same communication channel.Therefore, they interfere with each other. A typical communicationobjective is for the receiver to receive the transmitting signal from aspecific user with whom the receiver wants to communicate. In order toachieve this objective, multiple access systems are used. Typicalmultiple access systems are the Frequency Division Multiple Accesstechnology (FDMA), the Time Division Multiple Access technology (TDMA),and the Code Division Multiple Access technology (CDMA). Each multipleaccess system establishes its own rules for their users and uses basestations to regulate their users to achieve this objective.

One common problem frequently encountered in wireless communications isthe presence of interfering signals transmitted by devices other thanthe particular sender with which the receiver wants to communicate.Depending on the types of the wireless communications, interferences canbe classified in many ways. It may be intentional, such as the jammingof military wireless transmissions. It may be accidental and resultingfrom having multiple users who are sharing a common wireless channelwith or without the same base station that regulates the particularuser. The interferences resulting from users with the same base stationare called the multiple access interferences (MAI). All others arecalled the co-channel interferences. For simplicity, both interferencesare lumped into one word interferences.

The presence of interferences can severely compromise the ability of thereceiver to discern the signal from the intended sender, resulting in asignificant reduction of the channel data rate for the wirelesstransmissions from the sender to the receiver. In the cellular system,multiple access systems have been used to combat the multiple accessinterference with the support of a base station. The three commonly usedmultiple access technologies are the FDMA, the TDMA, and the CDMA. InFDMA, the users are assigned non-overlapping frequency slots (by thebase station), and hence the multiple access interference can beavoided. Similarly, in TDMA the users are assigned non-overlappingtime-slots, and in CDMA users are assigned ‘non-overlapping’ orthogonalcodes. Because of the power limitation of the base station, the area ofthe cell it controls is limited to its neighborhood. Therefore, any useroutside the cell can not be controlled by this base station, and hencemay interfere with the users in the cell.

Interferences in wireless transmissions are also a serious issue forWireless Local Area Network (LAN). A wireless LAN uses part of thefrequency spectrum that is free to everybody and hence it costs nothingto use the spectrum. It uses the internet to reach the outside world andhence it again costs nothing. However, the interferences between theusers can be significant because this part of spectrum is unregulated.This is one of the major challenges for wireless LAN. The currenttechnology confines it to be in a local area with limited users. It doesnot allow it to be developed to reach its full commercial potentialvalue. WiFi is one kind of Wireless LAN and hence shares the sameadvantages and challenges. Interferences between the users also exist inad hoc network, a closed wireless communication network but without abased station for central command.

The number of users that is allowed within a fixed spectrum is alsolimited by the interference. Each company is assigned a total spectrumfor its exclusive use. According to its multiple access system, thetotal spectrum is then divided into a number of “personal spectrums”.These personnel spectrums are preferred to be non-overlapping so thatthere are no interferences between users. This limits the number ofusers that is allowed within a fixed spectrum. However, higher data ratewould demand a wider personal spectrum for the users. This could causeserious interferences between the users because of the heavy overlappingof their personal spectrums. Therefore, an effective way of blockingthese interferences would have the potential of increasing the number ofusers within a fixed spectrum.

In view of the foregoing, there is a vital need for a way to effectivelycounter the negative effects of interfering signals and to enhance thechannel data rate of wireless communications between a sender and areceiver in the presence of interfering signals, and to increase thenumber of users within a fixed spectrum.

With the thirst of ever increasing higher data rate by demand, thecurrent multiuser wireless communications systems have difficult tofulfill the challenge for future generations of multiple access systems.For example, the required data rate for digital voice is less than 64Kbps, Standard Digital TV (SDTV) is 3-6 Mbps, and High Definition TV(HDTV) is 18-24 Mbps. On the other hand, the data rate of 2 G cellularsystem is about 140 kbps that is enough to support digital voice andtext transmission. The 3 G standards call for data rates up to 2 Mbpswhich can support the transfer of SDTV. Future wireless dataapplications such as broadband Internet access, interactive 3D gaming,and high quality audio and video entertainment, each of them may requirea date rate of 1-5 Mbps, which is much higher than current cellularphone system can provide.

The invention of the specific MIMO multiple access system described inthis patent application can reduce substantially the interferences atthe receiver and hence increases significantly the channel data rate,without the increase of spectrum bandwidth. A positive consequence ofthis is the increase of number of users within a fixed spectrum.

BRIEF SUMMARY OF THE INVENTION

The presented invention provides a multiple access system andalgorithms, called the Autocorrelation Division Multiple Access system(ADMA) and ADMA Algorithms, which substantially block interferences atthe receiver; thereby allowing the channel data rate to be significantlyimproved. This multiple access system and the algorithms provide animplementation of the Noise-Transparent Autocorrelation MatchingAnalysis given in U.S. patent application Ser. No. 11/002,161.

In the invention of ADMA System, the signal of each user is encoded witha unique code, called the ADMA code. The coded signal, called the ADMAsignal, is used for the transmission through the wireless channel to thereceiver from one or more transmitting antennas. The receiver receives aplurality of input signals by using, for example, two or more receivingdevices (e.g., antennas or smart antennas). Each received signalcontains a signal component that is from the designated user signalcorresponding to wireless transmissions from an intended sender, and aninterference component that is from one or more interferencescorresponding to wireless transmissions from other users (i.e. multipleaccess interference) and/or to co-channel interference sources. Thesignal component is then extracted from the received signals by afilter, called the ADMA Filter, by which the interference component issubstantially blocked. This is possible because the filter is designedto be orthogonal to the channel vectors of interferences. In thisinvention the ADMA filter is obtained without the knowledge of thechannel vectors of interferences which sometimes are neither known tothe receiver nor can be accurately estimated using pilot signaltechniques under heavy interferences. Finally, the designated signal isrecovered from the signal component by a decoder, call the ADMA decoder.

According to the invention, the ADMA filter is derived in the followingway: Each user signal is first coded with a unique ADMA code. Then thecoded signal is used to be transmitted through the channel. TheNoise-Transparent Autocorrelation Matching Analysis is then implementedat the receiver by applying specially designed algorithms to the uniqueADMA code assigned to the designated signal, by which the ADMA filter isobtained. The filter obtained is of a high degree of accuracy becausethe accuracy is not compromised by the noise. The algorithms and theADMA codes are part of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scenario of the wireless communications. The wireless LANsystem is represented by the computer users 1 and 2 and the wirelessrouter. The mobile system is represented by the mobile phone users 1, 2,3, and a base station not shown in the Figure. Any two users cancommunicate with each other via the wireless router, the base station(not shown) or via the internet (not shown). Besides the mobile phonesystem and wireless LAN system, the same spectrum is also shared byBluetooth and remote controller users. These users cause co-channelinterference to the mobile phone and wireless LAN systems. Thecommunication between any pair can be interfered by other users.

FIG. 2 is the schematic diagram of the ADMA System, showing anembodiment of the invention in which the channel data rate of wirelesscommunications between a sender and a receiver is enhanced by an ADMAfilter that blocks interference signals in accordance with theinvention.

FIG. 3 is the schematic diagram of the ADMA Filter and its ControlModule, showing an embodiment of the invention in which the interferencecomponent of the received signal (3-1) is substantially blocked by theADMA Filter at the receiver in accordance with the invention.

FIG. 4 is the schematic diagram of the ADMA transmitter showing anembodiment of the invention in which the user signals are coded by ADMAencoder to make them ADMA signals that is used to be transmitted intothe channel in accordance with the invention.

FIG. 5 is the schematic diagram of the ADMA receiver showing anembodiment of the invention in which the component of interferences ofthe received signals is blocked by the ADMA Filter to give the componentof the signal from which the desired user signal is obtained by the ADMADecoder, in accordance with the invention.

FIG. 6 provides an illustration on how multiple ADMA transceivers may bepositioned with respect to each other and to co-channel interferences ina typical multi-user wireless system.

FIG. 7 is the ADMA Encoder for Natural ADMA Code implemented by aFeedforward Shift Register

FIG. 8 is the ADMA Decoder for Natural ADMA Code implemented by aFeedback Shift Register.

FIG. 9 is the Feedforward Shift Register in the general form to bedesigned for the ADMA Encoder for a PLI ADMA code.

FIG. 10 is the Feedback Shift Register in the general form to bedesigned for the ADMA Decoder for a PLI ADMA code.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS I. Description of the ADMASystems

The ADMA System has the potential to be used to almost all wirelesssystem, such as cellular systems, wireless LAN, and ad hoc systems. InFIG. 1, the mobile system is represented by mobile phone user 1, 2, 3,and a base station (not shown). Any two mobile users can communicatewith each other via the base station. The Ad Hoc system is representedby mobile user 1, 2, and 3 but without base station. The wireless LANsystem is represented by two computer users 1, 2 and the wirelessrouter. Any two computer users can communicate with each other via thewireless router. Any communication between a pair of users (the solidline) can be interfered by any other user (dotted line) includingBluetooth user and remote controller user.

A cellular system is a closed mobile system that operates in a (private)licensed spectrum. No other user without the license can operate in thisspectrum. Therefore the interference from outside of the system can bekept to a minimum. However, limited spectrum put a limit on the numberof users to be operated at the same time. Any extra users would becomeinterferences to others. Therefore, one way to increase the number ofusers beyond this limit is to have a new multiple access system that canreduce these interferences.

From another point of view, wireless communication in the unlicensedspectrum such as in 2.4 GHz, where is operated by wireless LAN,Bluetooth, wireless remote controller and microwave oven. All thesesystems can operate in this spectrum without a license. Therefore,interferences can be a major concern which put a direct impact to thedata rate. It is needed to have a new multiple access system that canreduce these interferences.

ADMA is a multiple access system that substantially reduces theinterference and hence increases the number of users in the licensedspectrum and increases the date rate in the unlicensed spectrum. ADMAcan be implemented by one or more computer processors. The instructioncan be stored on a computer readable medium such as hard drive or flashmemory.

1. The Architecture of ADMA System:

By invention, the architecture of the Autocorrelation Division MultipleAccess system (ADMA) is shown in FIG. 2. It consists of the ADMATransmitter (2-2 and 2-11; also, 4-2 and 4-4 in FIG. 4), the ADMAReceiver (2-12, 2-6, and 2-8; also 5-1, 5-3, 5-5 in FIG. 5) and thewireless channel (2-4). The ADMA Transmitter consists of the ADMAEncoder (2-2; also 4-2 in FIG. 4) and the multiple-antenna transmittingsystem (2-11; also 4-4 in FIG. 4). The ADMA Receiver consists of themultiple-antenna receiving system (2-12; also 5-1 in FIG. 5), the ADMAFilter and the Control Module (2-6; also 5-3 in FIG. 5), and the ADMADecoder (2-8; 5-5 in FIG. 5). The ADMA Filter and its Control Module isimbedded in (2-6) for FIG. 2, and described in detail in FIG. 3 as (3-2)and (3-4) respectively.

The autocorrelation of a signal u(t), denoted by ρ_(u)(τ) is a sequenceof numbers that is uniquely determined by the signal itself.Mathematically, it is defined by

ρ_(u)(τ)=Ex{u(t)u*(t−τ)}, for τ=0, 1, 2, . . .

where u* is the complex conjugate of u, Ex{ } is the expectationoperator, and τ is called the time-lag variable of the autocorrelation.The significance of the autocorrelation of a signal is that it carriesthe information of the power distribution of the signal in the frequencyspectrum.

Noise signal n exists everywhere and it is a major handicap for wirelesscommunication. The distribution of noise signal is white and Gaussianwith variance ρ_(n) ². Therefore, its autocorrelation, denoted by ρ_(n)has the property that

${\rho_{n}(\tau)} = \left\{ \begin{matrix}\sigma_{n}^{2} & {{{for}\mspace{14mu} \tau} = 0} \\0 & {{{for}\mspace{14mu} \tau} > 0}\end{matrix} \right.$

Note that the autocorrelation of noise is zero on the set of time-lagvariables, τ>0, or τ=1,2, . . . . This set of time-lag variables iscalled the noise-transparent set because the autocorrelation of noise iszero on this set. We will later show as an invention how the computationof the ADMA filter is performed on the noise-transparent set and hencethe accuracy of the computation is not much compromised by the noise.

2. The ADMA Transmitter

The ADMA Transmitter first assigns each user a unique identificationnumber, called the ADMA code. By invention, these ADMA codes arespecially designed and the Natural code, the Pairwise LinearlyIndependent code and the Zero-Block code are presented. The nextobjective of the ADMA transmitter is to transform each user signal to acoded signal, called the ADMA signal in such a way that theautocorrelation of the coded signal is the same as the respective ADMAcode on the noise-transparent set of time-lag variables. These ADMAsignals are then transmitted by the multiple-antenna transmitting systemto the wireless channel.

Each user signal is fed into a respective encoder, called the ADMAencoder (2-2). The ADMA encoder transforms the user signal into a codedsignal, called the ADMA signal. By invention, the ADMA encoder isdesigned in such a way that the autocorrelation of the ADMA signal on anoise-transparent set is the same as the ADMA code assigned to therespective user. Therefore, each ADMA signal carries an identificationnumber in the form of ADMA code, and these ADMA signals are thentransmitted by the multiple-antenna transmitting system (2-11) into thewireless channel (2-4). Based on these ADMA codes, the receiver is ableto identify the ADMA signals.

Among the user signals, one of them is the designated one (heavy 2-1)that is the one the receiver intends to communicate with.Correspondingly, the designated ADMA signal is then transmitted togetherwith other ADMA signals through the wireless channel (2-4). Theco-channel interferences (2-10) are then mixed with these ADMA signalsin the wireless channel.

3 The ADMA Receiver

In the receiving side, at least two received signals (2-5) are receivedby multiple-antenna (at least two) receiving system (2-12). Each of thereceived signals (2-5) is a mixture of ADMA signals, the co-channelinterferences (2-10) and the noise (not shown). One of the ADMA signalsis the designated one. These received signals are then fed into thereceiver of ADMA. The function of the receiver is to isolate the desireduser signal from other user signals and co-channel interferences byimplementing the Noise-Transparent Autocorrelation Matching Analysis onthe multiple received signals as shown in U.S. Pat. No. 7,376,394.

The receiver of ADMA contains at least four components: the multiplereceiving antennas (2-12), the ADMA Filter (3-2), the Control Module(3-4) and they are all limped in (2-6), and the ADMA decoder (2-8).

There are at least two received signals from at least two antennas. Eachreceived signal is a mixture of all the ADMA signals and the co-channelinterferences. As shown in FIG. 3, all these received signals (3-1) arefed into a filter, called the ADMA Filter (3-2). The output (3-6) ofADMA Filter is a weighted sum of these received signals (3-1). Theobjective of the ADMA Filter is to assign proper weights to the incomingreceived signals, in such a way that all signals other than thedesignated ADMA signal are essentially cancelled and only the designatedADMA signal is retained essentially in the output of the ADMA filter.

The function of the Control Module (3-4) of the ADMA Filter is tocompute and instruct (3-5) the ADMA filter (3-2) its proper weight. Thisis achieved by the invention ADMA algorithm to match the autocorrelationof the output signal of the filter to the designated ADMA code on thenoise-transparent set, with the information of the input signals (3-1)and the output signal (3-6) of the ADMA Filter and the ADMA code of thedesignated users (3-3) As such, based on the U.S. patent applicationSer. No. 11/002,161 on Noise-Transparent Autocorrelation MatchingAnalysis, the proper weight of the ADMA Filter is computed and itsaccurately is not much compromised by the noise. Consequently, all theADMA signals other than the designated ADMA signal and the co-channelinterferences are substantially blocked. Hence, the output of the ADMAFilter consists of essentially the designated ADMA-signal (2-7).

This designated ADMA signal is then fed into the ADMA decoder (2-8). Thefunction of ADMA decoder is to perform the inverse of the ADMA encoder.Therefore, with the designated ADMA signal as its input, its out isessentially the designated user signal (2-9).

4. Multi-User System with ADMA Transceivers

A typical implementation of ADMA is illustrated in FIG. 6. In the closedmulti-user system, each user uses an ADMA transceiver (6-1). Each ADMAtransceiver is assigned an ADMA code known to all the transceiver in theclosed system. There is an ADMA transmitter (6-2) and an ADMA receiver(6-3) built in the transceiver. The co-channel interferences aretransmitted from separate sources (6-5). The communication between anytwo users (transceivers) is represented by the heavy double headerarrow, while the interferences from other users (multiple accessinterference) and co-channel interferences are represented by solidarrows. By using of the ADMA transceivers, the communication between anytwo users will have little interferences.

II. Components of ADMA Systems

The invention Autocorrelation Division Multiple Access system (ADMA) isa multiple access system that includes (1) ADMA Code, (2) ADMA Encoder,(3) ADMA Filter, (4) Control Module of ADMA Filter, and (5) ADMADecoder. The combination of them creates an implementation of thenoise-transparent Autocorrelation Matching Analysis, in the followingmanner. At the transmission side, as an invention all transmittingsignals are ADMA signals each of which carries the identification, orthe ADMA code of the respective user signal. At the receiving side, thereceived signals from the multiple-antenna receiving system are theinput to the ADMA Filter. Based on the invention, this filter isadjusted and determined by its Control Module in such a way that theautocorrelation of the output of the filter matches the designated ADMAcode on a noise-transparent set of time lag values. Based on U.S. patentapplication Ser. No. 11/002,161 on noise-transparent AutocorrelationMatching Analysis, the ADMA Filter substantially removes theinterference components from the received signal.

In the following, as an illustration of the general method, some of theADMA codes, their ADMA matching algorithms and their ADMAencoder/decoder are given. As an invention, the ADMA codes given belowhas the property that the weights of ADMA Filter can have a closed formsolution computed by ADMA algorithms. The first ADMA system is givenbelow:

(1) The Natural ADMA Code (2-13)

Each user who accesses the ADMA system is assigned a uniqueidentification number, called the ADMA code (2-13). An ADMA code C is asequence of say K numbers, represented by

C=(c ₁ ,c ₂ , . . . c _(k))

For N number of users (2-1), there will be N number of ADMA codes,represented by

C _(i)=(C _(i1) ,c _(i2) , . . . , c _(iK)),i=1,2, . . . , N

where C_(i) represents the ADMA code for the i^(th) user. The design ofADMA codes is unique.

As an invention, the natural ADMA codes is first presented here,

$\begin{matrix}{C_{1} = \left( {{1,0,0},\ldots \mspace{11mu},0} \right)} \\{C_{2} = \left( {{0,1,0},\ldots \mspace{11mu},0} \right)} \\{\vdots \;} \\{C_{N} = \left( {{0,0\mspace{14mu} \ldots}\mspace{11mu},{0,1}} \right)}\end{matrix}$

The i^(th) user is assigned the i^(th) ADMA code C_(i).

(2) ADMA Encoder (2-2) for Natural ADMA Codes

In order to achieve a better data rate, the user signals are usuallychosen to be white with unit variance.

As an invention, the ADMA encoder is designed to transform the usersignal to an ADMA signal the autocorrelation of which is the same as theADMA code of the user signal on the noise-transparent set. Specifically,the i^(th) ADMA Encoder (2-2) for natural ADMA codes is a shift registeras shown in FIG. 7. The input signal to the shift register is the i^(th)user signal u_(i) and the output signal s_(i) of the shift register isthe ADMA signal for the i^(th) ADMA encoder. The mathematical relationbetween the two is given by

${S_{i}(t)} = {{2{u_{i}(t)}} + {\frac{1}{2}{u_{i}\left( {t - i} \right)}}}$

It can be shown that for any user signal u_(i), the autocorrelation ofthe output signal s_(i)(t), denoted by ρ_(s) _(i) (τ) is the same as thei^(th) natural code C_(i) on the noise-transparent set, i.e., for τ=1,2,. . .

${\rho_{s_{i}}(\tau)} = \left\{ \begin{matrix}1 & {{{for}\mspace{14mu} \tau} = i} \\0 & {{{for}\mspace{14mu} \tau} \neq i}\end{matrix} \right.$

So, the i^(th) ADMA Encoder converts any i^(th) user signal to an ADMAsignal of which the autocorrelation is the same as the i^(th) ADMA code.

(3) ADMA Filter (3-2)

From the received signals x (3-1), the objective of ADMA filter w (3-2)is to compute in its output y (3-6) a weighed sum of the receivedsignals by

y(t)=w ^(H) x(t)=w ₁ x ₁(t)+w ₂ x ₂(t)+ . . . +w _(L) x _(L)(t)

where (x₁, x₂, . . . , x_(L)) are the L number of received signals and(w₁, w₂, . . . , w_(L)) are the L number of weights that are to bedesigned. Each received signal x_(i)(t) is a mixture of the ADMA signalsand co-channel interferences. A proper weight is one that yields in theweighted sum y(t) essentially the designated ADMA signal.

(4) Control Module of ADMA Filter (3-4)

The essential objective of the Control Module (3-4) is to compute theproper weight of the filter. Based on the U.S. patent application Ser.No. 11/002,161 on Noise-Transparent Autocorrelation Matching Analysis,this is achieved by computing the weight w so that the autocorrelationof the filter output signal y(t) is the same as the ADMA code on thenoise-transparent set.

As an invention, the computation of the proper weight is given infollowing steps. First, find a matrix R that contains all theinformation concerning all the interferences but not the designateduser. Then, find the proper weight w such that Rw=0.

Let the first user be the designated user.

1. From the receiver signal x(t) (3-1), compute the matrix R, by theEquation shown below

$R = {\sum\limits_{k = 2}^{N}{{Ex}\left\{ {{x(t)}{x^{H}\left( {t - k} \right)}} \right\}}}$

Note that the case k=1 is omitted from the summation because the firstuser is the designated user. The matrix R contains all the auto- andcross-correlations of all the interference signals, but not that of thedesignated user.2. The proper weight w is found by the equation

Rw=0

Therefore, all the auto- and cross-correlations of all the interferencesignals are eliminated by the filter w, but not that of the designateduser. The filter w is derived as follows. Do singular valuedecomposition (SVD) on the matrix R, i.e.,

$R = {{\left\lbrack {U_{1}U_{2}} \right\rbrack \begin{bmatrix}\Lambda_{11} & 0 \\0 & 0\end{bmatrix}}\begin{bmatrix}V_{1}^{H} \\V_{2}^{H}\end{bmatrix}}$

where V₂ εC^(L×L−(M+N−1)). Then Construct the filter by

w=αV₂z

for any zεC^(L−(M+N−1)), where α=((V₂z)^(H)R_(x)(τ₁)(V₂z))^(−1/2). Itcan be shown that any filter w so constructed provides the properweight. As such, the output of the filter is essentially the designatedADMA signal.

When the solution w in Step 2 is not unique, choose the best solutionaccording to some criterion, such as the maximum signal-to-noise ratio.

(5) ADMA Decoder (2-8)

As an invention, the ADMA Decoder performs the inverse of the ADMAencoder. The ADMA decider for Natural code is a shift register as shownin FIG. 8. Mathematically, it can be represented by the equation,

${{\hat{u}}_{1}(t)} = {{\frac{1}{2}{y(t)}} - {\frac{1}{4}{{\hat{u}}_{1}\left( {t - \tau_{1}} \right)}}}$

where the input of this decoder is the output signal of the filter y andits output is denoted by û₁, which is the estimation of the designateduser signal u₁. It can be shown that when the input signal is thedesignated ADMA signal, its output is essentially the designated usersignal.

It can be shown that the ADMA system with Natural ADMA code, so are theones given below, satisfies the conditions for the noise-transparentAutocorrelation Matching Analysis. Therefore, the ADMA filtersubstantially removes the interference component from the receivedsignal.

III. Alternative Implementation of ADMA Systems

As an invention, two families of ADMA codes are given here. They are (A)the Pairwise Linearly Independent ADMA code and (B) the Zero-Block ADMAcode. As an invention, they can be encoded by either the Shift RegisterMethod or the Insertion Method, followed by specially designed ADMAalgorithm and decoded respectively by Feedback Shift Register method orthe Deletion method.

There are alternative ADMA codes other than the natural ADMA code. Twoof them are given in here as part of the invention. They are thePairwise Linearly Independent (PLI) ADMA code as the ones given in (A)and (B), and the zero-block code as the one given in (C). There are alsodifferent ways to encode a user signal to give a specified ADMA code.Two methods are given here. They are (A) the Shift Register method and(B) the Signal Insertion method. There are also different ways todecoder a specific ADMA signal to give the user signal. The InverseShift Register method is used to decode the ADMA signals obtained by theShift Register method, and the Signal Deletion method is used to decodethe ADMA signals obtained by the Signal Insertion method.

A The Pairwise Linearly Independent (PLI) Codes (1) ADMA Codes (2-13)

As an invention, the family of pair-wise linearly independent (PLI) ADMAcode is presented. Consider a set of ADMA codes in the general form

C _(i)=(c _(i1) ,c _(i2) , . . . , c _(iK)) for i=1,2, . . . , N

where K is the length of the code. The set of codes is pair-wiselinearly independent (PLI) if no two codes in the set of N ADMA codesare linearly dependent. This is a very large family of codes. Almost anyarbitrarily chosen set of codes is PLI. The natural code is a specialcase of PLI code. Once a specific PLI code is chosen, assign a uniqueADMA code to each user.

(2a) ADMA Encoder-Shift Register (2-2)

Given an ADMA code, there are many ways to design an ADMA encoder. Oneway is to design a shift register to fulfill the purpose of ADMAencoder. The general form of shift register is shown in FIG. 9. Theinput of the shift register is the user signal u(t) and its output isdenoted by s(t). The mathematical relation for the general shiftregister is given by,

s(t)=α₀ u(t)+α₁ u(t−1)+ . . . +α_(P) u(t−P)

As an invention, the coefficients (α₀, α₁, . . . , α_(P)) of the Shiftregister is chosen so that the autocorrelation ρ_(s)(τ) of the outputs(t) is the same as the given ADMA code

C=(c ₁ ,c ₂ , . . . , c _(K))

on a noise-invariant set of time-lag variables, i.e., ρ_(s)(τ)=c_(τ) forτ=1,2, . . . K. As such, the shift register converts the user signal toits ADMA signal. Such ADMA encoder exists because the shift registerthat implements the natural codes given in FIG. 7 is a special case.

(2b) ADMA Encoder—Insertion Method

For a given ADMA code, C=[c₁ c₂ . . . c_(K)], the ADMA encoder requiresthe autocorrelation ρ_(s)(τ) of the ADMA signal s(t) to match the codewords of the ADMA code on the noise-transparent set, i.e.,ρ_(s)(i)=c_(i) for τ=1,2, . . . , K.

In a more general setting, the matching criterion of the ADMA encodercan be applied on a selected noise-transparent set τ=τ₁,τ₂, . . . ,τ_(K)>0. For example, the set can be a set of odd numbers τ=1,3,5, . . ., L, or a set of even numbers τ=2,4,6, . . . , L. In this more generalsetting, the ADMA encoder requires the autocorrelation ρ_(s)(τ) of theADMA signal s(t) to match the code words of the ADMA code on theselected noise-transparent set, i.e., ρ_(s)(τ)=c_(i) for τ=τ₁,τ₂, . . ., τ_(K).

As an invention, the Insertion method for the ADMA encoder is presentedin the more general setting. Given an ADMA code C=[c₁ c₂ . . . C_(K)],the objective of Insertion method is to insert more code words into theuser signal u(t) in such a way that the autocorrelation of the resultingsignal s(t) is the same as the ADMA code at a selected time-lagvariables on the noise-transparent set τ=τ₁,τ₂, . . . , τ_(K)≧0, i.e.ρ_(s)(τ_(j))=c_(j) for j=1, 2, . . . , K.

As part of the invention, a particular insertion sequence for theinsertion method is presented here. We first construct a sequenced^(T)=[d₁ d₂ . . . d_(K)], whose circular convolution at the time-lagvariables 1, 2, . . . , K is the same as a given ADMA code C in thefollowing way,

Step 1 From the given ADMA code C, construct a vector {tilde over (c)}by inserting a reflecting image of C as shown

$\overset{\sim}{c}:=\begin{bmatrix}{A\; \vdots \; c_{1}} & c_{2} & \ldots & {c_{K}\; \vdots \; c_{K}^{*}} & \ldots & c_{2}^{*} & c_{1}^{*}\end{bmatrix}$

where A is a positive value that satisfies

${A \geq {2{\sum\limits_{k = 1}^{K}{C_{k}}}}},$

and α* denote the complex conjugate of α.Step 2 Take discrete Fourier transform of {tilde over (c)}, i.e.

{tilde over (c)} _(F) :=DFT({tilde over (c)})

Step 3 Construct the vector d_(F) whose elements are square roots ofrespective elements of {tilde over (c)}_(F).Step 4 Calculate inverse discrete Fourier transform of d_(F), i.e.d:=IDFT(d_(F)).It can be shown that the circular convolution at the time-lag variables1, 2, . . . , K is the same as a given ADMA code CStep 5 We now insert the sequence d alternatively into a given usersignal u(t) in the following way: insert the first element of d betweenthe 1^(st) and the 2^(nd) position of u(t), the second element of dbetween the 2^(nd) and 3^(rd) position of u(t), and so on until allelements of d exhausted. Then repeat the above to the end of usersequence. The resulting sequence is the ADMA signal s(t) in the generalsetting on a selected noise-transparent set for τ_(k)=2 k. It can beverified that

${\rho_{s}\left( \tau_{j} \right)} = {{{Ex}\left\{ {{s(t)}{s^{*}\left( {t - \tau_{j}} \right)}} \right\}} = \frac{c_{j\;}}{4\left( {K + 1} \right)}}$

for j=1, 2, . . . , K, i.e., the autocorrelation ρ_(s) of the ADMAsignal s(t) at the even number of noise-transparent set τ_(j)=2j is sameas the j^(th) code word of the ADMA code, c_(j), by a constant factor

$\frac{1}{4\left( {K + 1} \right)}.$

(3) ADMA Filter (3-2)

The ADMA Filter for the PLI codes is same one as that for the NaturalCodes

(4) Control Module of ADMA Filter (3-4)

As an invention, we present the ADMA algorithm for the ADMA signals onthe selected noise-transparent set τ=τ₁, τ₂, . . . , τ_(K). Let thedesignated user be the first user. The ADMA Filter for the designatedADMA signal s₁ is computed by the following steps:

1 From the receiver signal x(t)(3-1), compute the covariance matrixR_(x), i.e.

R _(x)(τ)=Ex{x(t)x ^(H)(t−τ)} for τ=τ₁,τ₂, . . . , τ_(K)

2 Find the null-space of the designated ADMA code, C₁ ^(T):=[c₁₁ C₁₂ . .. C_(1K)]^(T) in the following way. Use the SVD algorithm to find thesingular value decomposition of

$C_{1}^{T} = {U\begin{bmatrix}{C_{1}^{T}}_{2}^{2} \\0 \\\vdots \\0\end{bmatrix}}$

where U is an unitary matrix. Decompose

U = [u₁⋮ U₂]

where u₁ is the first column of U and U₂ consists of the remainingcolumns.3 Project the ADMA codes other than the designated one, C_(i) ^(T),i≠1,on the null space of the designated ADMA code C₁ ^(T) obtaining p_(i),for i≠1

p _(i) :=U ₂(U ₂ ^(H) U ₂)⁻¹ U ₂ ^(H) C _(i) ^(T) for i=2,3, . . . N

4 Construct the matrix R by:

${R ::} = \begin{bmatrix}{\sum\limits_{k = 1}^{K}{P_{2,k}^{*}{R_{x}\left( \tau_{k} \right)}}} \\{\sum\limits_{k = 1}^{K}{P_{3,k}^{*}{R_{x}\left( \tau_{k} \right)}}} \\\vdots \\{\sum\limits_{k = 1}^{K}{P_{N,k}^{*}{R_{x}\left( \tau_{k} \right)}}}\end{bmatrix}$

where p_(i,k)* denotes the conjugate of the k^(th) element of p_(i). Thematrix R has the property that the elements of covariance matrix of thedesignated user for τ=τ₁,τ₂, . . . , τ_(K) are not included, andinformation of the auto- and cross-correlation matrices of theinterferences are kept.5 Calculate a vector w that satisfies

Rw=0

It can be shown that the vector w is the ADMA filter for the designatedADMA signal.

(5) ADMA Decoder (2-8)

(5a) The ADMA Decoder for the Shift Register Method is a feedback ShiftRegister. The general form of feedback shift register is shown in FIG.10. The input to the feedback shift register y(t) is the output of theADMA filter. The output signal û(t) of the feedback shift register isgiven by

û ₁(t)=b ₀ y(t)+b ₁ û ₁(t−1)+b ₂ û ₁₂(t−2)+ . . . +b _(P) û ₁(t−P)

In order for the feedback shift register to be the ADMA encoder, thecoefficients (b₀,b₁, . . . , b_(P)) have to be designed so that itperforms the inverse function of the ADMA encoder. Therefore, when theinput is the ADMA signal, its out should be the user signal. Thefeedback shift register given in FIG. 8 for the natural code is aspecial case.

The ADMA decoder for the Insertion method is simply by deleting somecode word from the output of the ADMA Filter s(t). In particular, theuser sequence u(t) can be obtained from s_(i)(t) by simply deleting theinserted symbols of d at positions 2, 4, 6, . . . The attraction of theInsertion Method is the simplicity of the decoder.

B The Zero-Block ADMA Code (1) Zero-Block ADMA Code (2-13)

As an invention, a zero-block code is presented here. Consider a set ofN number of codes in the general form,

C _(i)=(c _(i1) ,c _(i2) , . . . , c _(iK)) for i1,2, . . . , N

where K is the code length. A zero-block code is obtained by assigningeach code, say the i^(th) code a zero-block I_(i) and non-zeroeselsewhere in the code, i.e.,

$c_{ij}\left\{ {\begin{matrix}{= 0} & {{{for}\mspace{14mu} j} \in I_{i}} \\{\neq 0} & {{{for}\mspace{14mu} j} \notin I_{i}}\end{matrix}.} \right.$

The zero-blocks are not necessarily continuous. Further, the zero-blockssatisfy the overlapping rule that every zero-block overlaps with thenon-zero blocks of another, i.e., I_(i)∩Ī_(j)≠φ for every i≠j. Thenatural code is a special case of zero-block code. The advantage ofzero-block code is in the simplicity of its ADMA algorithm.

(2) ADMA Encoder (2-2)

The ADMA encoder for the zero block codes can be either the ShiftRegister Method or the Insertion Method.

(3) ADMA Filter (3-2)

The ADMA filter for the zero-block code is the same as the one forNatural code.

(4) Control Module of ADMA Filter (3-4)

The Control Module for Zero-Block code is the same as the one for PLIcode, except that the matrix R is computed by the equation below

$R = {\sum\limits_{i \in I_{1}}{{Ex}\left\{ {{x(t)}{x^{H}\left( {t - \tau_{i}} \right)}} \right\}}}$

The advantage of the zero-bloc code is the simplicity of the ADMAAlgorithm.

(5) ADMA Decoder (2-8)

The ADMA decoder for the zero-block code is the same as that for the PLIcode.

1. A method of transmitting data in a multiple access communicationsnetwork, the method comprising: generating a unique autocorrelationdivision multiple access (ADMA) code, from a set of ADMA codes such thatno pair in the set are linearly dependent, for reducing interference ina data transmission to at least one user device connected to themultiple access communications network; sending the unique ADMA code forthe user device from a transmitter to a receiver; encoding an originaldata stream using an ADMA encoder using the unique ADMA code such thatan encoded data stream is created; transmitting the encoded data streamto the receiver; filtering interference from the encoded data stream toobtained a substantially interference-free encoded data stream using anADMA filter which is a closed form solution derived by anoise-transparent autocorrelation matching analysis and incorporatingthe unique ADMA code; and decoding the substantially interference-freeencoded data stream by an ADMA decoder such that the original datastream is substantially obtained.
 2. The method of claim 1 furthercomprising storing the unique autocorrelation multiple access code foreach user device connected to the multiple access communicationsnetwork.
 3. The method of claim 1 wherein the step of encoding theoriginal data stream further comprises an ADMA encoder that isinvertible and that has the property that the autocorrelation of theencoded data stream is the same as the unique ADMA code on anoise-transparent set of time-lag variables.
 4. The method of claim 1wherein the step of encoding the original data stream further comprisesusing an ADMA encoder that is invertible and that has the property thatthe autocorrelation of the encoded data stream is the same as the uniqueADMA code on a noise-transparent set of time-lag variables.
 5. Themethod of claim 1 wherein the filtering step further comprises computinga weighted sum of the encoded data stream.
 6. A computer readable mediumhaving computer executable instructions for transmitting data in amultiple access communications network having a remote node forgenerating a unique autocorrelation division multiple access (ADMA) codefor reducing interference in a data transmission to at least one userdevice connected to the multiple access communications network andencoding an original data stream using an ADMA encoder using the uniqueADMA code such that an encoded data stream is created, the computerexecutable instructions comprising instructions for receiving the uniqueADMA code from the remote node; instructions for receiving the encodeddata stream from the remote node; instructions for filteringinterference from the received encoded data streams to obtained asubstantially interference-free encoded data stream using an ADMA filterwhich is a closed form solution derived by a noise-transparentautocorrelation matching analysis and incorporating the unique ADMAcode; instructions for decoding the substantially interference-freeencoded data stream by an ADMA decoder such that the original datastream is substantially obtained.
 7. The computer readable mediumaccording to claim 6 wherein the instructions for filtering interferencefurther include instructions for computing a proper weighted sum of thereceived encoded data streams.
 8. The computer readable medium accordingto claim 6 wherein the instructions for encoding further compriseinstructions for implementing an ADMA encoder that is invertible andthat has the property that the autocorrelation of the encoded datastream is the same as the unique ADMA code on a noise-transparent set oftime-lag variables.
 9. A system for transmitting data in a multipleaccess communications network, the system comprising: a transmitter nodecomprising a processor configured to generate a unique autocorrelationdivision multiple access (ADMA) code for reducing interference in a datatransmission to at least one user device connected to the multipleaccess communications network and an encoder configured to receive anoriginal data stream and produce an encoded data stream using an ADMAencoder and the unique ADMA code for the at least one user device; theat least one user device comprising: a receiver configured to receivethe encoded data stream from the transmitter node; an ADMA closed formfilter derived by a noise transparent autocorrelation matching analysis,the ADMA closed form filter incorporating the unique ADMA code andproducing a substantially interference free encoded data stream; adecoder that produces a substantially the original data stream from thesubstantially interference-free encoded data stream.
 10. The system ofclaim 9 wherein the multiple access communications network is one of acellular network, a computing network having a router or an ad hocnetwork.
 11. The system of claim 10 wherein the at least one user deviceis a computer.
 12. The system of claim 9 wherein the transmitter node isone of a computer router or a cellular base station.